c. 1600, "fleshy mass at the back of the testicles," Modern Latin, literally "that which is on the testicles," from Greek epididymis, a word probably coined by Greek anatomist Herophilus (c. 353-280 B.C.E.) from epi "on" (see epi-) + didymos "testicle," literally "double, twofold" (adj.), from PIE root *dwo- "two." An acceptable Englishing of it is in Richard Brome's "The Court Beggar" (1652):

Strangelove. I doe not slight your act in the discovery,
But your imposture, sir, and beastly practise
Was before whisper'd to me by your Doctor
To save his Epididamies